hs-CRP: the inflammation marker with the most outcome data

C-reactive protein (CRP) is made by the liver in response to inflammatory signals, chiefly interleukin-6 (see the IL-6 page). A standard CRP test is built to catch the large rises of infection and inflammatory disease. The high-sensitivity assay, hs-CRP, measures the same protein accurately at low concentrations, the range where it tracks cardiovascular risk. It is reported in mg/L. Some labs report CRP in mg/dL, which is ten times smaller as a number: 0.3 mg/dL is 3 mg/L.

The guideline numbers

These categories describe population risk, not disease. MedlinePlus notes that most healthy adults have CRP under 3 mg/L. Claims online that "optimal" hs-CRP is under 0.5 mg/L have no guideline behind them. The data below show a continuous gradient, and the categories are simply where the guideline writers drew lines.

What raises and lowers it

• Short-term rises: infections, including a cold you barely noticed, injuries, dental problems, surgery, flares of arthritis or gut inflammation, and hard or long exercise.
• Chronic rises: excess body fat, especially visceral fat, smoking, poor sleep, and chronic inflammatory disease.
• Lowers: weight loss, regular moderate exercise, stopping smoking, statins.

What it predicts

The Emerging Risk Factors Collaboration pooled 160,309 people without vascular disease from 54 prospective studies (Lancet, 2010). Per threefold higher CRP, the risk of coronary heart disease was 1.63 times higher adjusted for age and sex, 1.37 after adjusting for conventional risk factors, and 1.23 after also adjusting for fibrinogen. CRP was linked just as strongly with death from non-vascular causes, which is a hint that it marks general ill health as much as arteries. These are associations.

The trial that made hs-CRP clinically relevant was JUPITER (NEJM, 2008): 17,802 people with normal LDL but hs-CRP of 2 mg/L or more were randomised to rosuvastatin or placebo. Major cardiovascular events fell by 44%. In CANTOS (NEJM, 2017), canakinumab, an antibody against interleukin-1 beta, lowered hs-CRP without changing lipids in 10,061 people after a heart attack, and the 150 mg dose cut major cardiovascular events (hazard ratio 0.85), with more fatal infections. Together they suggest inflammation is part of the causal story, not just a bystander.

On GLP-1 drugs and weight loss

CRP was a prespecified secondary endpoint in STEP 1 to 3. At week 68, semaglutide 2.4 mg lowered CRP by an estimated 44% relative to placebo in STEP 1 (95% CI 39 to 49%), 39% in STEP 2 and 48% in STEP 3, and the fall tracked weight loss. For retatrutide, which is investigational, a post hoc analysis of a phase 2 trial in people without diabetes reported a 54.8% placebo-adjusted fall in hs-CRP over 48 weeks. The GLP-1 blood work page puts these next to the lipid changes.

How to test

• Ask for hs-CRP specifically if the purpose is cardiovascular risk.
• Be well. No infection, injury or vaccination in the previous two weeks, and no hard training in the 48 hours before.
• Two results. The AHA/CDC statement suggests averaging two measurements, ideally two weeks apart. hs-CRP varies a lot from week to week in the same person.
• Over 10 mg/L: repeat once you are well. It usually means something acute is going on.
• Fasting is not required, but drawing with the rest of a fasting panel keeps conditions consistent.

Tracking it in Peptide AI

In Peptide AI, hs-CRP sits in the inflammatory panel. The app reads it from a lab PDF or manual entry, scores the panel from 0 to 100 alongside an overall grade, flags values that warrant prompt physician consultation, and plots each result against your dose timeline. Because a single spike is common, note any illness or hard session in the days before the draw. Log the draw date, whether you fasted, and anything unusual in the days before, such as illness, a hard session or a dose step, so the next result is compared like with like. Bloodwork tracking shows the series next to the dose log, weight and side effects, and the panels page lists every marker the app groups. More markers are in the bloodwork guides.